1. Field of the Invention:
This invention relates to a method and apparatus for removing gas from the interior of a hollow-fiber permeability apparatus in which a permeating region of a housing contains a bundle of hollow fibers, and materials can selectively permeate through the membranes formed by the permeable walls of the hollow fibers, between first and second fluids flowing through the housing inside and outside the fibers respectively, and more particularly to a method and apparatus for removing gas from the interior of a hollow-fiber permeability blood dialysis apparatus of the dry type by which bubble removing operation before use for blood dialysis can be remarkably improved. These apparatuses are also known in the trade as hemodialyzers.
2. Description of the Prior Art:
Recently, blood dialysis apparatus for artificial kidneys, having permeable walls of, for example, cellulose, are widely used, greatly assisting patients suffering from renal failure.
As well known, blood dialysis is effected a few times per week for a patient suffering from chronic renal failure, so as to prolong the life of the patient or return the patient to the social life. In the present blood dialysis apparatus, permeable membranes of cellulose in the form of film or tube are piled, wound or bundled to obtain the total membrane area of about one square meter. The dialysate contacts with blood through the membranes.
The permeable membranes are dipped into water or impregnated with plasticizer such as glycerin in order to maintain a desired selective permeability of the permeable membranes, in the blood dialysis apparatus. In the blood dialysis apparatus of the wet type, the permeable membranes are dipped into water. And in the blood dialysis apparatus of the dry type, the permeable membranes are impregnated with plasticizer. A so-called "plate type" blood dialysis apparatus having piled permeable films, and a so-called "coil-type" blood dialysis apparatus having tubes wound into coil are generally of the dry type, and sterilized with ethylene oxide gas or with irradiation of .gamma.-ray.
Recently, hollow-fiber permeability apparatus have become popular in which hollow fibers formed into capillary tubes having an inner diameter of several hundreds microns are used. The most remarkable advantages of the hollow fiber permeability apparatus are that it provides a relatively large effective surface area of membrane and that the blood priming volume can be smaller than the coil-type and plate-type blood dialysis apparatus. The hollow-fiber permeability apparatus can be smaller-sized, and is superior in withstanding pressure and in security. In the hollow-fiber permeability blood dialysis apparatus, the hollow fibers are dipped into formalin, or it is impregnated with plasticizer and sterilized with ethylene oxide gas. Thus, hollow-fiber permeability apparatus of both types are marketed.
Before the blood dialysis apparatus is used for blood dialysis, it is required that blood flow path be filled with physiological saline solution. Such an operation is called a "bubble-removing operation". When the blood dialysis is started in the condition that many air bubbles (fine air bubbles) remain in the blood dialysis apparatus and circuits connected to the blood dialysis apparatus, there is the risks that the air bubbles would enter into the blood vessel of the patient during dialysis, disturb a preferable flow from the view point of hydrodynamics, cause thrombus, and/or reduce the effective membrane area.
In the coil type blood dialysis apparatus, the tubes are pressed flat to purge air therefrom. Accordingly, when physiological salin solution is introduced into the blood dialysis apparatus, there is little problem in the air-bubble removing operation.
In the bubble removing operation of the plate-type blood dialysis apparatus, the apparatus is inclined or vertically placed, and physiological salin solution is introduced into the blood flow path from below the apparatus. Thus, the air bubbles can be easily removed.
In most of the marketed hollow-fiber permeability apparatus, the hollow fibers are dipped into formalin. Fine bubbles are previously removed from the interiors of the hollow fibers. It is relatively easy to remove little bubbles remaining in the interiors of the hollow fibers. However, it requires a long time to remove and wash formalin from the hollow fibers, and a simpler system is desired. Moreover, the apparatus containing the formalin is unduly heavy and inconvenient for handling.
Recently, hollow-fiber permeability apparatus of the dry type are marketed which overcome the disadvantage of the hollow fiber permeability apparatus containing formalin. However, it requires a long time and much labor to purge fine bubbles from the interiors of the hollow fibers when physiological saline solution is introduced into the apparatus before use for dialysis.
It has been proposed to utilize carbonic acid gas in order to perfectly fill the blood flow path with physiological salin solution. In that method, air bubbles are substituted with carbonic acid gas in the blood flow path. Carbonic acid gas has a high water-solubility, and so it is easily dissolved into physiological saline solution. Accordingly, the blood flow path is perfectly filled with physiological saline solution.
There are some problems with this system since, in practice, a liquefied carbonic acid gas container is brought into a dialysis room. Carbonic acid gas is blown into the dialysis apparatus. Such a procedure is laborous and the use of high pressure gas is not preferable from the viewpoint of security. Besides, sealed dialysis apparatus previously containing carbonic acid gas are proposed for market. Such a dialysis apparatus has the remarkable inevitable disadvantage that some carbonic acid gas leaks out from the apparatus and is substituted with air, before use.